The use of polyester films for electrical insulation applications is prior art. The ever more stringent requirements relating to complexity of the circuits within a small space, together with the need to be able to produce these circuits rapidly, flexibly, and at low cost places stringent technological requirements on the film and on the steps within further processing.
Conventional processes for producing flexible circuits mostly relate to the full-surface metalization of the film web or lamination of the film web to metal foil and subsequent structuring of the resultant conductive surfaces by various processes, e.g. etching or mechanical removal of the undesired quantities of metal. There are also processes in which an embossment/print is applied to the metal, or a conductive paste composed of carbon/silver is applied. Disadvantages of these processes lie in their low flexibility and precision, which results in a relatively large separation between the conductor tracks, and/or the high costs associated with these processes, and/or the low production rates.
EP-A-1 274 288 describes a process in which laser irradiation is used to form copper nuclei from copper-containing metal oxides, and a subsequent electroplating step deposits further copper on the nuclei. That specification describes exclusively injection-molded parts, and there is no indication as to how and whether the process can be applied to polyester films and films generally. In particular, there is no indication of the nature of the polymers and additives needed to permit production of oriented films. The PBT/SiO2/spinel compounded material described in EP-A-1 274 288 is unsuitable for producing oriented films because the high crystallization rate of the polybutylene terephthalate used and the high level of filling with fumed silica prevent reliable processing of this polymer.
In particular, there is no indication as to how it is possible to produce a film with adequate dimensional stability under conditions of local heating after irradiation with electromagnetic radiation and further processing.